Yes, in those movies, the hot white guys (and sometimes girls) usually ride on top of the muscular horses. So when you want to show a horse riding a man as a visual gag, why not make the man a hot white guy with a gruff beard?

You act as though they first decided to make an image representing Westerners and then chose that particular scene as an intentional insult, but you need to consider that they likely made thousands of test images, most of which were just playing around with the model's capabilities and not specifically crafted for the announcement post.

So why did this one get picked? I think it boils down to the visual gag being funny and the movie-like quality.